Ultrastructural effects of silicic acid on primary lung fibroblasts in tissue culture

Transmission and scanning electron microscopic examination of primary lung fibroblasts exposed in tissue culture to polymeric silicic acid (PSA) revea led profound cellular changes in the cell surface membranes, resulting in r apid endocytosis of affected membranes and formation of multivesicular bodi es. Exposure to monomeric silicic acid did not appear to exhibit any immedi ate adverse effects. Appearance of numerous cytoplasmic vacuoles within 1 h of PSA exposure was easily visible by light microscopy. Electron microscop y revealed that PSA exposure caused formation of an 'osmiophilic' cell surf ace membrane. Numerous osmiophilic cytoplasmic blebs on the surface and sub sequent endocytotic vesicles appeared to collapse and aggregate into multiv esicular bodies. This study provides ultrastructural evidence of the direct interaction between lung fibroblasts and polymeric silicic acid, which has a dramatic effect the surface membrane, its subsequent internalization and cytoplasmic processing. This interaction could be one of the key steps in the damaging effects of silica containing dust. (C) 2001 Harcourt Publisher s Ltd.